Arizona weekly citizen., 1887-11-19
TESTING A GREAT LENS.
VISIT TO THE WORKSHOP OF THE
 LATE AVIAN CLARK.

LATE AVIAN CLARK.
 Finishing the Object Glass of . Great
 Teleseope-PoIishinxw with the raIxp ot
 the HAnd-A Peep at a st.r-A
 Story.
 In 1882 I called to see Alvan Clark, the distinguished constructor of telescopes, who has just died found him at bis home Tn Cambridgeport, MaSa His sons were busy putting the finishing touches to the great telescope object glass then being made for the Russian Astronomical observatory as Pulkova. The Pulkova objective was to be plnced .n a temporary mounting that very evening to bo tested for the first time on celestial objects
 It Is in tho after correction and pcrfecting of the objective which calls for the special skill which has made Alvan Clark's name so famous The large Objectives. such ss tue Pu'Eova and Lick glasses, are ground and polished by machinery. Two levers work in opposite directions, and are so arranged that any part Of the glass surface may be rachel, doing the work. The final polish, which is of the most delicate nature imaginable, is done with the surface of the hand Mir Clark went So ia- a. to Say that one revolution of the hand in excess would change the correction.
 On table was the finished Pulkova lens. whicn weighed 4jO pounds, and consiste os two lenses each thirty inches in diam-ter. Generally thess lenses are made to accurately tt, and arc joined together with Canaia bal san,, but in such large glasses as the Pulkova and ihe Lick, tkcy are fitted in e metal frame with an adjustment so that they can bs male tO approach each other, or otherwise.
 Wien Intervening was sufficiently sdva5oed the gr-1t PulkOva glass was placed in its tenn porary fitting in tue garden. There was no moon and the darkness was tense. Tbe glass was brought out on four wheel hand tuck and littcl into the tube by five men and fixed by revolving 1t tn the screw fitting The tube WIS forty-fivo feet lorg and weighci with the attending fittings about seven tons. Twopiles of patchwork supported the whole. There was no rlrckwork movement and tho rough ct apparatus was eu'p,oye,l, the teiescnps was raised and moved by guide rope. the mo tion of an equatnriai movement heinz mi tassd by using R common windlass. As the as,.icn of tue earth caused the object to paSs acruss the field of ihe telescope, the observer gave The or,rr -follp~," when a sligit turn of ths windl-Ss kept the object in view. Such were the rough appliances used tO test this e., ,oOO lena
 VIEW or A FIXED STAR
 The planets had all set, Gni had hc sat isfed with v.ew of a fixed stor, ,.' b Is an excellent object for testing the optics. proper ties of lens, but vory Gninteresting other wIss. us the larS, st telescope can make little impression on Q fixed star; no d'sk can be .fr of 1rr-Hf es.us lected was a small one, and barely ,iSible as a pale, minute object. On lookin: .: it with this magnificent instrument it's wonderful light gathering powers were at once evident, for the star sh0nc with the luster and brill fancy of an electric light. It was an object which brought out Hll the imperfections of the glass, and to the eyes of Mir. Clark and bis sons many were evident, and, it was said, two months work was necessary to correct them During the trial the lens were lowered and five men revolved the glass in is fitting. On its being placed in position again one of the sons was about tO make another test when the old mnn shouted: Wait, boys, let her cool"
 was curious to know what this could mean, and Alva Clark explained that the cor reciion was % delicate that the ieat from the hands of The five men holding the metal case of the objective would change the correction, 90 it had To "cool"
 In rolvCrsatiOn with Mir. Clark on the advantaScso of immense telescopes such as this one, he admitted that the telescopes of mod crate aperture, say from ten ts fifteen inches, were preferable for general use even for the highest purposes. He spoke with pride Ot such an instrument he had made, with which he had seen all that c Juld be seen sven with colossal telescopes. OHiy one dis covery has been made with the VOninGton telescope of twcnty-Six inches diameter during it's many years of use. The Kusslss Pu!kova instrument, delivered by the ClsI-' In 1882, has never been heard from, and those who expect immediate and extraordinary results from the Lick thirty-s;x inch objective will probably be disappointed. These huge tels scopes are great light gatherers and useful for photographs and spectroscopic work, but their definitions of the surface of the moon and the planets are disappointing.
 A story IS told of Q French astronomer who travelled hundreds of miles to look through the great Ross telescope. When asked what he would like tO see he called for the planet Saturn, which was then in good position. On looking through the telescope and finding the wretche,i definition of the object he said:
 sYou tell me have looked at the planet Saturn, so must believe have done SO; but was not aware of the fact. t."-John Michels in New York Sun.